Residents forced to leave their homes after toxic gas escapes.

Residents on the state's north have been evacuated from their homes after toxic fumes contaminated the air at Murwillumbah.

About 10 people were asked to leave their houses in the Bray Park area after a cleaning process at the nearby water treatment plant went wrong.

The fumes escaped from the Bray Park Water Treatment plant just after midday and council workers experienced minor eye and throat irritations.

The Tweed Shire Council's water manager, Anthony Burnham said the problems started when a chlorine tank was being cleaned out.

The tank was being decommissioned so the space could be used as a headquarters for the Murwillumbah Men's Shed.

Mr Burnham says human error caused the problems.

"We've made a mistake in respect to the concentrations to carry out that process and that's resulted in the production of toxic chlorine gas and some sulphur gases that then escaped from the tank," Anthony Burnham said.

Residents were given the all clear and were able to return to their homes about three hours after the incident.